So-called blow-pins are utilized to form hollow objects, such as containers, by a process known as blow-molding. A typical blow-pin assembly 10 is illustrated in FIG. 1. The blow-pin assembly 10 includes a circular body 12 having an outer circumferential surface 12a. The body 12 is disposed about a central axis C1. The body 12 defines a circular groove 14 proximate the outer circumferential surface 12a. The body 12 also defines a central passage 16. A plurality of through holes 18 are disposed between the groove 14 and the central passage 16. The through holes 18 place the groove 14 in fluid communication with the central passage 16.
The blow-pin assembly 10 further includes an O-ring 20. The O-ring 20 is disposed within the groove 14, as shown in FIG. 1. The O-ring 20 is typically formed from an elastic material such as rubber.
The blow-pin assembly 10 is used in conjunction with a thermoplastic parison 22 having a neck portion 22a (for clarity, only the neck portion 22a is shown in FIG. 1). The blow-pin assembly is used in conjunction with a hollow mold (not shown). The neck portion 22a is positioned over the body outer circumferential surface 12a during blow-molding operations. The remaining portion of the parison 22 is positioned within the mold. Pressurized air is directed into the parison 22 by way of the central passage 16, in the direction denoted by the arrow 24. The pressurized air causes the parison 22 to expand. The parison 22 expands until it contacts the inner surfaces of the mold. Contact with the inner surfaces restrains the expanding parison 22, and thereby causes the parison 22 to assume the shape of the mold.
The groove 14 is pressurized during blow-molding operations. More specifically, pressurized air from the central passage 16 pressurizes the groove 14 by way of the through holes 18. Pressurization of the groove 14 urges the O-ring 20 outward, into the parison neck portion 22a. This contact inhibits leakage of air from the pressurized area within the parison 22. More specifically, the O-ring 20 inhibits leakage of pressurized air between the parison neck portion 22a and outer circumferential surface 12a.
O-rings such as the O-ring 20 have substantial disadvantages when utilized in the above-described application. For example, the elastic material from which the O-ring 20 is formed typically experiences chafing after repeated usage. Such chafing reduces the useful life of the O-ring 20. This characteristic necessitates frequent replacement of the O-ring 20 when the blow-pin assembly 10 is utilized in high-rate-of-production applications. Frequent replacement of the O-ring 20 increases the operating cost of the blow-pin assembly 10, and can result in costly interruptions in the production process. Furthermore, O-ring chafing reduces the sealing effectiveness of the O-ring 20. A reduction in sealing effectiveness can lead to quality-control problems associated with insufficient air pressure within the parison 22 during blow-molding operations.
In light of the above discussion, a need exists for a blow-pin assembly having an improved sealing mechanism. In particular, the sealing mechanism should be more durable than commonly-used seals. The present invention is directed to this goal.